According to JP-A-11-294203, a throttle body receiving a disc-shaped throttle valve and a substantially round bar shaped throttle shaft is integrally molded of a resinous material, so that weight of the product and production cost are reduced. The throttle body includes a cylindrical bore wall part that internally forms an intake air passage. The throttle valve opens and closes the intake air passage. The throttle valve is supported by a valve holding portion formed in the throttle shaft. The bore wall part of the throttle body has a first and second boss portions (bearing supporting portions) that are formed in the circumferential periphery of the bore wall part. Cylindrical bearings are assembled into the first and second boss portions of the bore wall part to rotatably support the throttle shaft. In this throttle apparatus, the throttle shaft is rotatably supported by first and second sliding holes respectively formed in the first and second bearings, so that the throttle shaft is restricted from moving circumferentially. However, the throttle shaft is not restricted from moving axially in its thrust direction.
In general, an angular sensor is provided in the throttle apparatus to detect a rotation angle of the throttle valve, i.e., throttle position. The angular sensor is constructed with a detecting element, such as a hall element and a magnet that is arranged to oppose to the detecting element. The magnet is provided on one axial end side of the throttle shaft. Therefore, when the throttle shaft moves in its thrust direction, accuracy of detection of the throttle position may be degraded. Accordingly, the throttle shaft needs to be properly positioned in the thrust direction.
Besides, when the throttle shaft is largely displaced in its thrust direction, the inner wall face of the bore wall part and the outer circumferential periphery of the throttle valve may interfere with each other when the throttle valve is in the vicinity of its full close position. Accordingly, scratch and chipping may be caused. Besides, the throttle valve and the throttle shaft may not be smoothly operated, and throttle position may not be promptly controlled corresponding to an accelerator position operated by the driver. As a result, drivability of the vehicle may be impaired. When airtightness of the throttle valve in its full close position is degraded, idling speed of the engine increases, and fuel efficiency may be impaired in an idling operation of the vehicle.
According to an example shown in FIG. 7, a throttle body 100 includes a first boss portion 101 and a second boss portion 102, into which a first bearing 104 and a second bearing 105 are respectively assembled. The first bearing 104 and the second bearing 105 respectively have a first shaft hole and a second shaft hole, through which the throttle shaft 103 penetrates. The throttle shaft 103 is axially inserted by thrust restricting means 111, 112 such as an E-ring and a C-ring. Specifically, the thrust restricting means 111, 112 are additionally assembled from both axial end sides of the throttle shaft 103. Thus, the throttle shaft 103 is restricted from moving axially with respect to the first boss portion 101 and the second boss portion 102. The throttle shaft 103 internally forms a rectangular hole (valve holding portion), into which the throttle valve 309 is inserted, so that the throttle valve 309 is partially received in the throttle shaft 103.
According to an example shown in FIG. 8, the throttle body 100 has the first boss portion 101, into which an outer ring of a ball bearing 106 is press-inserted. The throttle shaft 103 is press-inserted into an inner ring of the ball bearing 106. A needle bearing 107 is assembled into the second boss portion 102 of the throttle body 100. The throttle shaft 103 is press-inserted into the needle bearing 107, and a thrust restricting means 113 such as an E-ring and a C-ring is additionally assembled from axially end side of the throttle shaft 103 to restrict the throttle shaft 103 from moving axially with respect to the first boss portion 101 and the second boss portion 102.
In the above thrust supporting structure of the throttle shaft 103, additional assembling process is needed. Specifically, the throttle shaft 103 needs to be assembled into the bearing received in the first boss portion 101 and the bearing received in the second boss portion 102. Besides, the thrust restricting means 111, 112, 113 need to be additionally assembled to both axial ends of the throttle shaft 103 located in the vicinity of the bearings 104, 105, 106, 107. Accordingly, a number of components of the throttle apparatus increases, and an additional assembling process is needed. As a result, cost of the throttle apparatus increases.